Phonation threshold pressure is defined as the minimum subglottal pressure that is necessary to produce phonation for a given laryngeal configuration. Mathematical models and animal studies have suggested that phonation threshold pressure should increase with pathological phonation (Titze, J. Acoust. Soc. Amer., 85:901-6 (1989); Wexler et al., Annals Oto, Rhin. & Laryn., 98:668-73 (1989)). Phonation threshold pressure can be used as a measure of the ease with which phonation can be produced, and this measure should also be a clinically useful measurement in the evaluation of clinical voice disorders.
Many methods have been described to measure subglottal pressure: (1) directly by tracheal puncture (Isshiki, J. Speech Hear. Res., 7:17-29 (1964)); (2) directly using a miniature pressure transducer inserted through the nose and placed in the throat (Kitzing et al., Medical and Biological Eng., 13:644-8 (1975); Koike et al., Folia Phoniatr. (Basel), 20:360-80 (1968)); (3) indirectly using an intra-esophageal balloon (Lieberman P., Direct comparison of subglottal pressure and esophageal pressure during speech (Lieberman, J. Acoust. Soc. Am., 43:1157-64 (1968); Lieberman, J. Acoust. Soc. Amer., 45:1537-43 (1969); van den Berg, Folia Phoniatr. (Basel), 8:1-14 (1956)); (4) indirectly by placing a subject in a body plethysmograph (Tanaka et al., J. Acoust Soc. Amer., 73:1316-21 (1983); and (5) indirectly by measuring the intra-oral pressure (Hertegard et al., J. Voice, 9:149-55 (1995); Kitajima et al., Acta Otolaryngologica, 109:473-8 (1990); Lofqvist et al., J. Acoust. Soc. Amer., 72:63-5 (1982); Netsell, Phonetica, 20:68-73 (1969); Rothenberg, J. Speech Hear. Disord., 47:219-23 (1982); Smitheran et al., J. Speech Hear. Disord., 46:138-46 (1981); Kitajima et al., Acta Otolaryngologica, 113:553-9 (1993)). However, none of these methods are practical for routine clinical use. Further, direct measurement of subglottal pressure requires an invasive procedure and knowing the subglottal pressure is not, in most cases, sufficiently important for subjects or patients to agree to the risks of these invasive procedures.
One non-invasive technique for the measurement of subglottal pressure is the airflow interruption technique. Pressures measured using this technique have been compared to actual subglottal pressures measured by tracheal puncture in the same subjects, and good correspondence between the measurements has been reported (Nishida et al., Otologica Fukuoka, 10:264-70 (1964); Sawashima et al., Ann. Bull. RILP, 17:23-32 (1983); Bard et al., Ann. Otol. Rhino. Laryngol., 101:578-82 (1992)). Despite the promise of the airflow interruption technique, it is not yet in clinical use. There have been questions as to the relevance and usefulness of the measurements made with it to date for the diagnosis and evaluation of voice disorders and pathologies affecting the vocal tract.
A simple non-invasive technique for the clinical measurement of phonation threshold pressure would be desirable. One non-invasive technique for the measurement of phonation threshold pressure has been reported which involves the measurement of oral pressure using a translabial catheter. See Verdolini-Marston, et al., J. Voice, 4, 142-151 (1990). However, this technique is complex, requiring that subjects be trained for 5-10 minutes, and many test results have to be discarded because satisfactory results could not be obtained. No reports are known of the measurement of phonation threshold pressure using the airflow interruption technique.